from (photo) data to poles
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From (photo) data to poles. Ron Workman Data Analysis Center Institute for Nuclear Studies George Washington University. Baryons 2013 University of Glasgow. Some thoughts on N* photo-couplings. ● How do Breit -Wigner and pole photo-couplings compare? - PowerPoint PPT PresentationTRANSCRIPT
From (photo) data to polesRon Workman
Data Analysis CenterInstitute for Nuclear Studies
George Washington University
Baryons 2013University of Glasgow
Some thoughts on N* photo-couplings
● How do Breit-Wigner and pole photo-couplings compare?
● E2/M1 values are clearly different
● Some old pole values (VT) differ from more recent Bonn-Gatchina values.
● Is the similarity of Bonn-Gatchina pole/BW results dependent on model details?
A.V. Anisovich et al.,EPJ A48 (2012) 15
Pole andBreit-Wignervalues similarapart from aphase
Pole vs BW widthsvery different forS11 and P11
| Rπ | differentfrom current values
Quantities (real) evaluated at BW resonance energy
Quantities (complex) evaluatedat pole position
Photo-decay amplitudes from multipoles
C: isospin factor
SAID model for pion photoproduction ( 1990 )
Tππ gives phase (Watson’s Thm)
Phase determined by Tππ (smooth connection to Watson’s Thm)
0.054 phase: -115o
Simple case: Δ(1232) 3/2+
BG: ~ 0.052 phase: -125o
Largest contribution: E2 (pole)
Largest contribution: M1 (pole)
Pole vs BW contributions for Δ(1232)
Term → 0 for W = 1232 MeV( no contribution to BW + background approach )
Don’t expect approaches to be similar for E2/M1
RLW, R.A. Arndt,PRC 59, 1810 (1999)
~ linear
0
Dominant pieces for E2 and M1
A1/2 , A3/2 for Δ(1232) at the pole
Some comparative results for A1/2 , A3/2
Breit-Wigner values extracted usinga form similar to MAID
Agreement with pole valuesis reasonable even for caseswith Rπ = Γπ / 2 being a poor approximation
plus
Some other background forms
Crawford/Morton ‘83Berends/Donnachie ‘78
Resonance Background
Arai/Fujii ‘82
Kamano et al., Dyn CC model
Large differences
Kamano et al., arXiv 1305.4351( May 2013)
Program is ambitious
Difficult to determinesource of differences inphoto-couplings:
Fit quality vs DCC
Obtaining the residues
● analytic continuation / contour integrals● speed plots● Padé approx● regularization method ● ‘Pietarinen expansion’
Zagreb/Tuzla
BW: technically simple – but model dependentPole: model independent – but new technical issues may arise
Laurent
Padé
Pietarinen
(Pere Masjuan)
(A. Svarc)
f b c ea
ae
c
f
Cut plane
Unit circle
See, for example,H. BurkhardtDispersion RelationDynamics, Ch. A9
Z
μb
Z0 ZC
Zagreb-Tuzla form
Z
Compare to:
F15
SAIDπNSP06
( A. Svarc )
Interesting results when applied to SES, with no analytic form available to determine poles
( A. Svarc )
Application tomultipoles isbeing studied
Other material
πN
For next speaker:2 fits with 1 or 2 D13 states
Characteristic forward peakingin charged-pion photoproduction
Feature is absent in this plot fromarXiv: 1305.4351v1